APPLICANT'S ABSTRACT: Due to high rates of unprotected intercourse with multiple partners, adolescents are at great risk for sexually transmitted diseases (STDs) including the human immunodeficiency virus (HIV) (American Association for World Health, 1998; Whaley, 1999). Alcohol use is commonly cited as a reason for high levels of risky sexual behavior among adolescents such as those involved in the criminal justice system (Brook, Balka, Abernathy, & Hamburg, 1994; Morris et al., 1998; Lowry, Holtzman, Truman, Kann, Collins, & Kolbe, 1994), largely because these adolescents evidence extremely high levels of both alcohol use and risky sexual behavior. However, the nature of this association has not been adequately demonstrated, the influence of third variables has often been neglected, and factors affecting the alcohol/risky sex connection have received little attention. The current research project will examine the complex association between alcohol and risky sexual behavior in a longitudinal design among a sample of 300 high-risk adolescents on probation. Hypotheses regarding both proximal and distal influences of alcohol on engaging in risky sexual behavior, as defined by engaging in vaginal intercourse without a condom, will be explored. Psychosocial determinants of condom use, personality characteristics, alcohol use history, and sexual behavior history will be assessed at an initial time point. A follow-up assessment of recent alcohol use and sexual behavior will be conducted six months after the initial measurement. The first specific aim is to establish whether a previously tested mediational model of intentions to use condoms (Bryan, Aiken, & West, 2000) predicts actual condom use behavior six months later among criminally-involved adolescents, irrespective of alcohol use. The second specific aim is to determine how quantity and frequency of alcohol use influences the relationships among model constructs and condom use by simultaneously estimating the model of condom use among heavy drinkers versus light drinkers/abstainers. The third specific aim is to examine the role of third variables that may account for the relationship between alcohol use and risky sex (e.g., impulsivity/sensation seeking, sex-related alcohol expectancies, and overall frequency of intercourse), and to assess via a within-subjects episodic methodology the degree to which alcohol use concurrent with sexual activity is proximally associated with lower rates of condom use. These findings will inform the development and implementation in the future of a theory-driven, empirically targeted HIV prevention intervention for adolescents with high rates of alcohol abuse and problems.